Police today charged one more of the 114 people arrested at a Nottingham school in April, in order to prevent a suspected protest at the coal-fired power station. This brings the number of environmental activists charged with conspiracy to commit aggravated trespass to 25 within the past month.

The move has left activists worried. Aggravated trespass is a summary offence, meaning it is always heard in the magistrates courts. It carries a maximum sentence of six months.

A charge of conspiracy to commit aggravated trespass carries a maximum six-month sentence, too.. But it is an indictable offence, which means the case will be heard in front of a jury in the crown courts, which is an incredibly expensive and time-consuming procedure.

Sometimes these cases – such as the conspiracy to commit public nuisance charge brought against members of the "No M1 Widening" campaign in 2007 – are just thrown out by the judges. But sometimes, as in the conspiracy cases against animal rights activists and anti-arms manufacturing campaigns, they are treated extremely seriously. The impact on the lives of the accused is enormous, because under the terms of a conspiracy charge, you can be forbidden to talk to anyone involved, which can involve housemates, family, friends. Your possessions can be seized (Julie White of the M1 campaign had her door broken down by police, her computer seized and held for a year, and even items taken off her washing line) and held on remand for the duration of the trial.

The decision to use a conspiracy charge against 27 climate change activists shows how, despite the police's attempts to brush up their image at this year's climate camp, they continue to use draconian powers to clamp down on the growing grassroots climate justice movement. The fact that hundreds of ordinary people are planning to take control of Ratcliffe-on-Soar power station next week is proof that such measures will not succeed.

Are they sending a wider message out to all activists? Nottinghamshire force, who made the arrests, says that it has no comment to make on the decision. But if this actually flies, if the court allows the case and convictions follow, it has catastrophic implications. Any activist involved with planning any kind of illegal direct action could be charged with conspiracy to commit aggravated trespass.

As White says: "You could pick up anyone you wanted. We're getting into thought crimes now." Is that what the police are after?